This invention relates to a power saving mode in a wireless telephone system.
Wireless telephones, using code division multiple access (CDMA) modulation techniques or other analog frequency modulation (FM) based wireless systems such as the Advanced Mobile Phone System (AMPS), may be operated in a standby mode to conserve power provided by a battery. During the standby mode, wireless telephones often continuously receive and monitor a stream of signaling data messages sent by a base station while waiting to receive a telephone call. One of these data message streams is on a forward overhead control channel (FOCC).
An FOCC message, shown in FIG. 1, includes a dotting word, a word-sync, and repeating words A and B. The wireless telephone uses the dotting or bit-sync word to synchronize the phone hardware to the clock of the data message. The word-sync indicates the present location in the data stream to the wireless telephone and that the data sequence is about to start. Also imposed on the message data stream are busy-idle bits, each of which is sent between every ten bits of the message to indicate the status of the system channel. The repeat words A and B each contains 40 bits, and each word is repeated five times in the message. The wireless phone receives both of these words but only processes one of them. If the wireless phone""s Mobile Identification Number (MIN) is even, word A is processed; otherwise word B is processed. However, in order to receive and process these words, the wireless phone""s receiver must be on and drawing power the entire time, thereby reducing the time a wireless, battery-powered telephone can be used for communication.
The present disclosure reduces the time that the receiver in the wireless telephone is on, and therefore drawing power, while in a standby mode. Wireless telephones that are particularly suited for this purpose include analog phones such as AMPS phones and other wireless devices that are capable of operating in multiple modes, such as the CDMA and the AMPS.
In one aspect, the disclosure features an improved method of reducing power consumption in a dual mode wireless phone, such as a CDMA/AMPS phone, that monitors messages from a forward overhead channel in a standby mode. The phone has a receiver that receives RF signals. The method includes turning the receiver off after decoding a pertinent word for the receiver in a particular message and turning it on again approximately one millisecond prior to a next pertinent word. The turn-on is initiated only if necessary to satisfy a redundancy check or if the next word is a beginning of a next message. The above steps are repeated for the next message.
In one embodiment, the redundancy check is satisfied if at least three out of five pertinent words are matched. In another embodiment, the redundancy check is satisfied if the pertinent word matches a previously defined control-filler message.
In another aspect, the disclosure features a circuit for providing a sleep state for both modes of the dual mode phone. The circuit includes a transistor having a base, a collector, and an emitter terminals, a supply voltage coupled to the collector terminal, a mode signal providing input to the base terminal, and a sleep signal providing input to the emitter terminal. When the sleep signal is asserted in a particular mode indicated by the mode signal, the collector terminal is driven to turn the receiver off.